The major purpose of this study is to investigate 1) affective states, neuropsychobiological patterns and general development of infants with a parent with bipolar illness; 2) To study the infant-family interaction, particularly the difference between the ill and healthy parent. There is general agreement about the genetic vulnerability of first degree relatives of manic-depressive patients. Such genetic vulnerability may possibly be already evident during infancy. The same may be said about environmental factors, especially the family, causing an affective disorder, which too, may be identified and detected by the study of infant-family interactions.